Various types of car HVAC units are known in the prior art. Most existing units are large, roof mounted units designed primarily for vans and campers. They are unsightly, and would look even more so on a normal passenger car. Air conditioning is often the primary function, and the units are intended for use while the vehicle is occupied, not unattended. What is needed, and what the present car roof automatic HVAC apparatus provides, is a more streamlined device that can be integrated into the roof of a normal vehicle to maintain the temperature inside the vehicle at a comfortable and safe level when left unattended, especially when a pet or child is left inside.